FIELD OF THE INVENTION
[0001] The invention relates to a cryogenic cooling system, in particular a cryogenic cooling
system with a self-supporting demountable insert.
BACKGROUND TO THE INVENTION
[0002] Cryogenic cooling systems are commonly used to perform experiments at low temperatures
below 100 Kelvin. Systems are generally customised for a specific experiment by installing
experimental apparatus in a particular arrangement. Installation of experimental apparatus
can be difficult and time consuming, commonly requiring the use of cranes or elevated
platforms to access the system. Furthermore, testing is generally required after the
installation of equipment to ensure it is functioning satisfactorily, which can take
a significant amount of time. The more time spent installing and troubleshooting,
the less time spent collecting experimental data.
[0003] Cryogenic cooling systems can reach millikelvin temperatures when in use, typically
by including a number of platforms which are held at intermediate temperatures between
room temperature and millikelvin temperatures. In this way, the cooling can be staged,
such that the final platform of the system can provide continuous cooling to millikelvin
temperatures. Installed experimental apparatus and other components of the system
can provide a path from room temperature to the final platform. In order to prevent
unintentional heating through these components, each platform provides a thermal sink
to remove additional heat.
[0004] It is possible for experimental services to be assembled on a module outside a system
and installed pre-assembled. This is typically faster than direct installation of
experimental services. However, it is important for the module to be well thermalised,
so that millikelvin temperatures can be obtained. In the prior art, thermalisation
is achieved using clamps and/or complex and extensive adjustment processes.
[0005] It is the case that a minor offset will result in poor thermalisation within the
system.
[0006] Low temperature physics experiments are becoming increasingly complex, and the experimental
services required to perform the experiments is consequently increasing. Quantum Information
Processing (QIP) experiments, for example, use radio-frequency (RF) wiring to address
devices with large numbers of qubits. As the number of qubits scales up, the amount
of RF wiring required correspondingly increases. Cryogenic cooling systems are expected
to accommodate the growing amounts of experimental services. One way the growing demands
can be accommodated is by providing modular upgrades for a core system. However, manufacturing
tolerances can accumulate to result in mismatched joints and poorly thermalised platforms
within the cryogenic cooling system, thus requiring extensive minor adjustments to
improve performance.
[0007] It is desirable to have a more convenient way of installing experimental services
in a cryogenic cooling system.
SUMMARY OF THE INVENTION
[0008] A first aspect of the invention provides a cryogenic cooling system comprising, when
in use: a primary insert comprising: a plurality of primary plates, each primary plate
having a primary contact surface; and one or more primary connecting members arranged
so as to connect the plurality of primary plates; a demountable secondary insert comprising:
a plurality of secondary plates, each secondary plate having a secondary contact surface;
and one or more secondary connecting members arranged so as to connect the plurality
of secondary plates such that the secondary insert is self-supporting; and one or
more adjustment members; wherein the one or more adjustment members are configured
such that, when in use, when the secondary insert is mounted to the primary insert,
the adjustment members cause the primary and secondary contact surfaces of the respective
primary and secondary plates to be brought into conductive thermal contact.
[0009] Advantageously, the system comprises adjustment members which cause the primary and
secondary contact surfaces of the respective primary and secondary plates to be brought
into conductive thermal contact with each other. This removes the need for numerous
minor adjustments to overcome a misalignment between two portions of a cryogenic cooling
system such that they are in effective thermal communication. When demounted, the
secondary insert can also be moved with respect to the primary insert as a self-supporting
body, which further simplifies the mounting and demounting process. For example, each
plate of the secondary insert can be aligned with respect to the corresponding plate
of the primary insert in a single step.
[0010] The one or more adjustment members may form part of the primary insert. In this case,
the adjustment members may form part of the plurality of primary plates, or form part
of the one or more primary connecting members, or form part of both the plates and
the connecting members. Similarly, the one or more adjustment members may form part
of the secondary insert. In this case, the adjustment members may form part of the
plurality of secondary plates, or form part of the one or more secondary connecting
members, or form part of both the plates and the connecting members. It is also possible
for the adjustment members to form part of the primary insert and the secondary insert.
Alternatively the adjustment members may take the form of fasteners that are configured
to couple corresponding plates of the primary and secondary inserts. The choice of
location of the adjustment members may depend on a specific implementation. For example,
if the secondary insert is designed to accommodate rigid experimental apparatus, the
position and type of adjustment member will be chosen accordingly.
[0011] The primary and secondary plates typically extend in a generally planar manner and
are connected in use along mutually adjacent peripheral surfaces of the plates, and
these may be stepped. Preferably, the conductive thermal contact between a primary
plate and the corresponding secondary plate is provided by area contact between conformal
planar regions of the respective primary and secondary contact surfaces. Each of the
primary and secondary plates may comprise a flange. When a primary plate is brought
into contact with the corresponding secondary plate, a lower surface of the flange
of the primary plate matches an upper surface of the flange of the secondary plate
to form a continuous structure. Typically, the primary plates and the secondary plates
are formed from a high conductivity material and thus a joint in which the plates
are intimately connected over a large area will provide a good thermal connection
across the joint.
[0012] The adjustment members typically cause the primary and secondary contact surfaces
of the respective primary and secondary plates to be brought into conductive thermal
contact by accommodating a misalignment between each of the plurality of secondary
plates of the demountable secondary insert and the corresponding primary plate of
the primary insert. There may be a misalignment between primary and secondary plates
as a result of manufacturing tolerances. Any misalignment between plates, if left
unadjusted, will reduce the thermal conductance between plates.
[0013] Although the cryogenic cooling system comprises both a primary insert and a secondary
insert, the secondary insert (or, alternatively, the primary insert) is demountable
and thus is removable from the system. When the secondary insert is in a demounted
state, the secondary plates are typically spatially positioned with respect to one
another in a secondary configuration. The secondary insert is self-supporting in its
demounted state, and the spacing between adjacent plates within the secondary insert
may be determined by the secondary connecting members. Similarly, when the secondary
insert is in a demounted state, the primary plates are typically spatially positioned
with respect to one another in a primary configuration. The spacing between adjacent
plates within the primary insert may be determined by the primary connecting members.
[0014] During a mounting process, the secondary insert may be mounted to the primary insert.
A plate of the secondary insert is preferably configured to be brought into contact
with a corresponding plate of the primary insert. However, there may be a misalignment
between the above-mentioned plates. The misalignment may be the offset between the
plane of a secondary plate and the plane of the corresponding primary plate in the
respective primary and secondary configurations. Each pair of plates may have a different
misalignment, and the misalignment may be positive or negative. Consequently, each
adjustment member may provide a different level of adjustment, and typically is capable
of providing a range of motion of at least 2 millimetres, preferably at least 4 millimetres
in order to accommodate the misalignment.
[0015] The secondary insert is demountable from the cryogenic cooling system. The secondary
insert may be fully demounted, i.e. all of the plates of the secondary insert may
be separated from the primary insert and removed. Optionally, the secondary insert
may only be partially demounted. If the secondary insert is partially demounted, some
of the plates of the secondary insert remain attached to the primary insert, whilst
the remainder of the plates of the secondary insert are removed from the primary insert.
Preferably, one or more of the secondary connecting members are removable such that
two or more of the plurality of secondary plates may be detached from the demountable
secondary insert as a unitary, self-supporting body or assembly.
[0016] The secondary insert may comprise a first secondary plate, a second secondary plate
and a third secondary plate connected using secondary connecting members, wherein
the second secondary plate is positioned between the first and the third secondary
plate. If the secondary connecting members connecting the second secondary plate and
the third secondary plate are removed, the second secondary plate and the first secondary
plate may be removed as a unitary structure. The partially demounted secondary insert
(the first and second secondary plates) is preferably self-supporting in a similar
way to the self-supporting nature of the fully demounted secondary insert.
[0017] The demountable nature of the secondary insert advantageously allows the secondary
insert to be modified away from the cryogenic cooling system. However, in cases in
which it is not necessary to remove the entire secondary insert, it may be beneficial
to leave a portion of the secondary insert attached to the primary insert. For example,
as low-temperature experiments are typically performed in a vacuum, one of the joints
between the primary insert and the secondary insert may form part of a barrier between
atmospheric pressure and low pressure. Therefore, additional sealing may be required
such as the use of an o-ring or other vacuum seal such as to reduce the possibility
of any gas leaks. It may be beneficial to leave the plates forming the above-mentioned
barrier in place to avoid repeatedly reforming the seal.
[0018] An advantage of the secondary insert being demountable from the cryogenic cooling
system is the ability to assemble, modify and test experimental services mounted to
the secondary insert away from the cryogenic cooling system. Furthermore, the modifications
may only need to be performed on two, or any number of, plates of the secondary insert.
It may be easier and therefore preferable to partially demount the secondary insert,
only removing the necessary plates.
[0019] Typically, experimental services are positioned within the cryogenic cooling system
and are used to perform experiments at low temperatures. Preferably, one or more the
plurality of secondary plates is configured to accommodate experimental apparatus.
This is particularly advantageous if the experimental apparatus mounted to the secondary
insert is complex and time-consuming to assemble. The experimental services can hence
be assembled and tested away from the cryogenic cooling system before being mounted
to the primary insert.
[0020] The cryogenic cooling system can be used for low temperature experimental procedures
and cooling can be achieved using a number of refrigeration apparatus. It is particularly
desired for such systems to achieve millikelvin temperatures. To this end, a dilution
unit preferably forms part of the cryogenic cooling system, for example the primary
insert may comprise a dilution refrigerator or components thereof. The dilution refrigerator
may be thermally coupled to one or more plates of the primary insert. Alternatively
the primary insert may comprise a helium-3 refrigerator or a 1 kelvin pot. In such
a way, one or more plates of the primary insert may attain millikelvin temperatures.
The conductive thermal contact between the primary insert and the secondary insert
ensures that the secondary insert may reach similarly low temperatures during operation.
[0021] One or more of the primary plates or the secondary plates may comprise a rigid portion
and one or more deformable portions. Preferably, the deformable portions are deformable
with respect to the rigid portions to accommodate the misalignment. The one or more
adjustment members may hence comprise the one or more deformable portions. During
the mounting of the demountable secondary insert to the primary insert, the one or
more deformable portions may locally deform so as to cause the conductive thermal
contact. The deformable portions of the plates may be provided at the plate edges,
for example in the form of flanges. One advantage of this mode of adjustment is the
ability to maintain the primary and/or secondary configurations within the respective
inserts. For example, operation of the adjustment member may not change the separation
between adjacent primary plates of the primary insert or adjacent secondary plates
of the secondary insert. In practice this means that the primary or secondary inserts
respectively can remain fixed and can therefore accommodate rigid experimental apparatus
which is mounted to more than one plate. Similarly, the separation between corresponding
plates of the primary and secondary inserts respectively can remain fixed. The deformation
may be configured to occur locally, in pre-defined areas of a plate, such that experimental
apparatus is not damaged, but conductive thermal contact is nevertheless achieved.
The deformable portions may form part of the primary plates. Alternatively, the deformable
portions may form part of the secondary plates. The deformable portions may optionally
form part of both the primary plates and the secondary plates.
[0022] When the secondary insert is in a demounted state, the primary and secondary inserts
may have respective primary and secondary configurations as described above. If the
adjustment is achieved through local deformation, it is possible for the primary and
secondary configurations to be maintained even when the demountable secondary insert
is in a mounted state. The one or more adjustment members may alternatively cause
one or both of the primary or secondary configurations to be adjustable so as to cause
the conductive thermal contact. For example, the one or more adjustment members are
configured to change the separation between adjacent primary plates or adjacent secondary
plates. This may be achieved by configuring each of the one or more primary connecting
members or secondary connecting members to deform so as to accommodate the misalignment
between plates.
[0023] The one or more adjustment members may form at least part of one or more of the primary
connecting members or secondary connecting members. For example, the one or more adjustment
members may form respective flexible portions of the primary or secondary connecting
members. During the mounting of the secondary insert to the primary insert, a misalignment
could be accommodated by placing the secondary connecting members under a compressive
or tensile load. In response to the load, the secondary connecting members would deform
thus causing the conductive thermal contact by bringing the secondary plate into alignment
with the corresponding primary plate. Similarly, a misalignment could be accommodated
through the deformation of flexible primary connecting members.
[0024] Alternatively, the one or more adjustment members may be configured to allow movement
of the one or more primary plates with respect to the one or more said primary connecting
members, or the one or more adjustment members may be configured to allow movement
of the one or more secondary plates with respect to the one or more said secondary
connecting members. For example, the primary or secondary connecting members may be
rotatable so as to change the separation between adjacent primary plates or adjacent
secondary plates using the one or more adjustment members. This adjustment may generally
be achieved where an end of the primary or secondary connecting members comprises
a screw or tapped portion. In this case the adjustment member may comprise said screw
or tapped portion of a connecting member in combination with a receiving member configured
to engage with the screw or tapped portion so as to adjust the separation between
adjacent plates of the primary or secondary insert.
[0025] Preferably, the primary and secondary connecting members are thermalised at the respective
primary and secondary plates. Typically there is a heat load conducted from room temperature
along the primary and/or secondary connecting members to the lower temperature stages
of the system. Thermalisation at the plates advantageously intercepts this heat load,
thereby forming a thermal sink that enables distal stages of the primary or secondary
insert to obtain lower temperatures during operation of the system. Effective thermalisation
of the primary connecting members may be achieved through the use of one or more primary
shims, each said primary shim thermally coupling a said primary plate to one or more
said primary connecting members and configured to allow movement of the said primary
plate with respect to the said one or more primary connecting members. Similarly,
effective thermalisation of the secondary connecting members may be achieved through
the use of one or more secondary shims, each said secondary shim thermally coupling
a said secondary plate to one or more said secondary connecting members and configured
to allow movement of the said secondary plate with respect to the said one or more
secondary connecting members.
[0026] Further aspects of the invention will now be described. Any features discussed in
connection with one aspect are equally applicable in respect of the remaining features
and each aspect shares similar advantages.
[0027] A second aspect of the invention provides a demountable secondary insert for use
in a cryogenic cooling system in accordance with the first aspect.
[0028] A third aspect of the invention provides a method of operating the system according
to the first aspect, wherein the secondary insert comprises a first secondary plate,
a second secondary plate and a third secondary plate, a first secondary connecting
member connecting the first secondary plate to the second secondary plate, and a second
secondary connecting member connecting the second secondary plate to the third secondary
plate, and wherein the primary insert comprises three primary plates, each said primary
plate corresponding to a respective secondary plate of the secondary insert, the method
comprising: mounting the secondary insert to the primary insert such that secondary
plates are thermally coupled to the corresponding primary plates using the one or
more adjustment members; and partially demounting the secondary insert from the primary
insert, wherein partially demounting the secondary insert comprises: removing the
first secondary connecting member from the secondary insert; and removing the second
secondary plate, the third secondary plate and the second secondary connecting member
from the primary insert as a unitary self-supporting assembly, without removing the
first secondary plate from the corresponding plate of the primary insert.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Embodiments of the invention will now be described with reference to the accompanying
drawings in which:
Figure 1 is a schematic illustration of a cryogenic cooling system in accordance with
a first embodiment of the invention;
Figure 2 is a perspective view of a cryogenic cooling system in accordance with the
first embodiment of the invention;
Figure 3 is an exploded side view of a cryogenic cooling system in accordance with
the first embodiment of the invention;
Figure 4 is a first exploded perspective view of a cryogenic cooling system in accordance
with the first embodiment of the invention;
Figure 5 is a second exploded perspective view of a cryogenic cooling system in accordance
with the first embodiment of the invention;
Figure 6 is an exploded view of a cryogenic cooling system in accordance with the
first embodiment of the invention with experimental services attached;
Figure 7 is a schematic illustration of a secondary plate from a cryogenic cooling
system in accordance with the first embodiment of the invention;
Figure 8(a) is a schematic illustration of part of a cryogenic cooling system in accordance
with the first embodiment of the invention before thermal connection is made;
Figure 8(b) is a schematic illustration of part of a cryogenic cooling system in accordance
with the first embodiment of the invention after thermal connection is made;
Figure 9(a) is a first schematic illustration of part of a cryogenic cooling system
in accordance with a second embodiment of the invention;
Figure 9(b) is a second schematic illustration of part of a cryogenic cooling system
in accordance with the second embodiment of the invention;
Figure 10(a) is a schematic illustration of part of a cryogenic cooling system in
accordance with a third embodiment of the invention before thermal connection is made;
Figure 10(b) is a schematic illustration of part of a cryogenic cooling system in
accordance with the third embodiment of the invention after thermal connection is
made;
Figure 11 is a first cross-sectional view of part of a cryogenic cooling system in
accordance with the third embodiment of the invention;
Figure 12 is a perspective view of part of a cryogenic cooling system in accordance
with the third embodiment of the invention;
Figure 13 is a second cross-sectional view of part of a cryogenic cooling system in
accordance with the third embodiment of the invention; and
Figure 14 is a perspective view of three exemplary secondary inserts for use in a
cryogenic cooling system in accordance with an embodiment of the invention.
DETAILED DESCRIPTION
[0030] Figure 1 provides a sectional view of the interior of a cryogenic cooling system
according to a first embodiment. The system comprises a plurality of thermal stages
1-5 and an outer stage 6. The thermal stages 1-5 and outer stage 6 are connected by
primary and secondary rods 17, 27, thus forming a tiered assembly in which the stages
are aligned and spatially dispersed along a central axis extending parallel to the
rods. The primary rods 17 are not shown in Figure 1 for clarity. The primary and secondary
rods 17, 27 are formed from a low thermal conductivity material such as stainless
steel. When in use, the thermal stages 1-5 are contained within a cryostat 36, which
is typically evacuated to improve the thermal performance by the removal of convective
and conductive heat paths through any gas within the cryostat 36. The cryostat 36
is mounted to the outer stage 6, and the outer surface 7 of the outer stage 6 is exposed
to room temperature and pressure and is formed from a low conductivity material.
[0031] The cryogenic cooling system comprises cooling apparatus. The cooling apparatus cools
the cryogenic cooling system from room temperature to an operational base temperature.
The cryogenic cooling system in the first embodiment is substantially cryogen-free
(also referred to in the art as "dry") in that it is not principally cooled by contact
with a reservoir of cryogenic fluid. However, despite being substantially cryogen-free,
some cryogenic fluid is typically present within the cryostat when in use, including
in the liquid phase, as will become clear. In this embodiment, the cooling is achieved
by use of a mechanical refrigerator and a dilution unit. The mechanical refrigerator
may be a pulse-tube refrigerator (PTR), a Stirling refrigerator, or a Gifford-McMahon
(GM) refrigerator.
[0032] In this embodiment, the mechanical refrigerator is a PTR 40, and is thermally coupled
to the first thermal stage 1 and the second thermal stage 2. Each thermal stage 1-5
is formed from a high conductivity material such as copper and has a different operational
base temperature. The first thermal stage 1 is thermally coupled to a first PTR stage
41 and attains an operational base temperature of about 50 to 70 kelvin. The second
thermal stage 2 is thermally coupled to a second PTR stage 42 and attains an operational
base temperature of about 3 to 5 kelvin. In this embodiment, the second PTR stage
42 forms the lowest temperature stage of the PTR 40.
[0033] The third thermal stage 3, fourth thermal stage 4 and fifth thermal stage 5 are thermally
coupled to a dilution unit 8. The cooling of the third, fourth and fifth thermal stages
3, 4, 5 is achieved through operation of the dilution unit 8, in which an operational
fluid is circulated around a cooling circuit 60. The operational fluid is typically
a mixture of helium-3 and helium-4. The operational fluid is pumped around the cooling
circuit 60 which comprises a condensing line 61 and a still pumping line 62 using
a compressor pump 63 and a turbomolecular pump 64. The operational fluid can be stored
in a storage vessel 65 and supplied to the cooling circuit 60 using a supply line
66. The third thermal stage 3 is thermally coupled to a still 10 which forms part
of the dilution unit 8. The operational base temperature of the third thermal stage
3 is typically 0.5 to 2 kelvin. The fifth thermal stage 5 is thermally coupled to
a mixing chamber 9 of the dilution unit 8. The operational base temperature of the
fifth thermal stage 5 is typically 3 to 30 millikelvin. The fourth thermal stage 4
forms an intermediary stage between the third and fifth thermal stages 3, 5 and has
an operational base temperature of about 50 to 200 millikelvin.
[0034] In use, a number of heat radiation shields 56-58 are attached to the thermal stages
1-5, wherein each shield encloses each of the remaining lower base-temperature components.
The first heat radiation shield 56, second heat radiation shield 57 and third heat
radiation shield 58 are attached to the first thermal stage 1, second thermal stage
2, and third thermal stage 3 respectively. This reduces any unwanted thermal communication
between the thermal stages 1-5 and allows the stages to attain different operational
base temperatures.
[0035] The cryogenic cooling system of Figure 1 can be controlled using a control system
50. The control system 50 is typically a suitable computer system, although it is
possible to have manual control of the system. The operation of each part of the system
can be controlled using the control system 50, including the operation of the PTR
40, the dilution unit 8, pumps 63, 64 and associated valves; the monitoring of temperature
and pressure sensors; and the operation of other ancillary equipment to perform desired
procedures.
[0036] A cryogenic cooling system as described can be used to perform experiments at low
temperatures, generally below 100 kelvin. Although not shown in Figure 1, experimental
services can be mounted within the cryostat 36. The choice of experimental services
and their particular arrangement within the cryostat 36 is customisable. One such
example of experimental services will be discussed with reference to Figure 6. Typically
a particular arrangement of experimental services is installed, tested, and remains
fixed for a period of time. Modification of the arrangement within the system to perform
a different type of experiment is typically very time consuming, requiring numerous
adjustments and troubleshooting procedures before the experiment can be run. Embodiments
of the invention provide a primary insert 18 and a secondary insert 28, wherein the
secondary insert 28 is demountable from the primary insert 18. Experimental services
can hence be mounted to the primary insert 18 or to the secondary insert 28, which
is easy to remove and reinstall, or to both the primary and secondary inserts 18,
28. The primary insert 18 comprises a plurality of primary plates and the secondary
insert 28 comprises a plurality of secondary plates 21-26, wherein each primary plate
is configured to fit to a corresponding secondary plate in order to form a respective
thermal stage 1-5 of the system, as will be further discussed.
[0037] An advantage of mounting the experimental services to the secondary insert 28 arises
from the ability to remove the secondary insert 28 from the cryogenic cooling system.
Assembly and preliminary tests can be performed 'on the bench', outside the cryogenic
cooling system in which the experiment will be performed. In this way, modifying or
updating the experimental services to run a different experiment can be performed
relatively quickly and easily. Low-temperature experiments using a cryogenic cooling
system such as a dilution refrigerator typically take days, weeks or months to perform.
Modifications to the experimental services within the system lead to experimental
down time, i.e. time during which the cryogenic cooling system is not at operational
base temperature, as the modifications typically need to be performed at room temperature.
The ability to manipulate experimental services on the demounted secondary insert
28 on the bench (remote from the system itself) reduces the experimental down time.
For example, multiple secondary inserts may be provided for use with a given cryogenic
cooling system. Adjustments may be made to experimental services on a first secondary
insert under atmospheric conditions whilst a cryogenic environment is maintained in
the system for performing experiments on a second secondary insert.
[0038] Embodiments of the invention also provide adjustment members which cause the primary
insert 18 and the secondary insert 28 to be brought into conductive thermal contact.
Good thermal contact is important to achieve when performing low temperature measurements.
In the presence of a heat flux, for example as generated by operation of a cooling
source, a temperature gradient will naturally arise between the primary insert 18
and the secondary insert 28. The difference in temperature between these components
will be proportional to the heat flux and inversely proportional to the thermal conductance.
For any practical experiment there is a limit to the heat flux that can be applied
to the system (as the cooling power available from either of the PTR stages 41, 42
or the dilution refrigerator 8 is finite). The thermal conductance of a joint will
vary depending on numerous factors including its temperature and contact pressure.
The adjustment members are typically configured to limit the temperature difference
between corresponding stages of the primary and secondary inserts 18, 28, for example
to within 2%, and preferably within 1%, of the absolute temperature of the higher
temperature stage. This is achieved by making the thermal conductance between these
stages sufficiently high. For example, where the second thermal stage 2 is cooled
to 4 kelvin by the second PTR stage 42 (at a cooling power of 1 watt), the adjustment
member for the second thermal stage 2 may ensure that the temperature difference between
corresponding primary and secondary plates of the second thermal stage 2 does not
exceed 40 millikelvin. The thermal conductance between primary and secondary plates
of the second thermal stage 2 is therefore approximately 25 W/K at 4 kelvin. Similarly,
where the fifth thermal stage 5 is cooled to 100 millikelvin by the mixing chamber
9 (at a cooling power of 400 microwatts), the adjustment member of the fifth thermal
stage 5 may ensure the temperature difference between corresponding primary and secondary
plates of the fifth thermal stage 5 does not exceed 1 millikelvin. The thermal conductance
between primary and secondary plates of the fifth thermal stage 5 is therefore approximately
0.4 W/K at 0.1 kelvin.
[0040] A variety of adjustment members are envisaged and embodiments facilitating different
methods of adjustment will be described.
[0041] Figure 2 shows the primary and secondary inserts 18, 28 from Figure 1 in further
detail. As shown, each thermal stage 1-5 comprises an inner primary plate 11-15, an
inner secondary plate 21-25, and an edge piece 31-35. The outer stage 6 comprises
an outer primary plate 16 and an outer secondary plate 26. Each of the inner and outer
secondary plates 21-25, 26 are connected to the corresponding inner and outer primary
plates 11-15, 16 along a peripheral portion of the secondary plates. Each of the edge
pieces 31-35 are connected to the corresponding inner primary plates 11-15 and the
corresponding inner secondary plates 21-25 along a peripheral portion of the respective
inner primary and secondary plates. The inner and outer primary plates 11-15, 16 are
connected by primary rods 17, and the inner and outer secondary plates 21-25, 26 are
connected by secondary rods 27. The primary and secondary rods 17, 27 extend between
the plates in a direction normal to the plates. In this embodiment, the edge pieces
31-35 are not connected, but in an alternative embodiment the edge pieces 31-35 may
be connected by edge rods extending between the edge pieces.
[0042] The inner and outer primary plates 11-15, 16 and primary rods 17 form part of a primary
insert 18. The inner and outer secondary plates 21-25, 26 and secondary rods 27 form
part of a secondary insert 28. The secondary insert 28 is demountable from the cryogenic
cooling system and, in particular, the primary insert 18. When the secondary insert
28 is in a demounted state, it forms a self-supporting assembly, which does not require
any additional support structures to maintain its original configuration and can be
removed from the primary insert 18 as a unitary body.
[0043] The designs of the secondary insert 28 and primary insert 18 are such that good thermal
contact will be achieved between any secondary insert 28 and primary insert 18 when
the secondary insert 28 is in a mounted state. It is important to ensure effective
thermalisation between corresponding plates in the primary insert 18 and secondary
insert 28 so that any cooling applied to one of the primary or secondary plates can
be effectively applied to the other of the secondary or primary plates.
[0044] Achieving good thermal contact between any secondary insert 28 and primary insert
18 when the secondary insert 28 is in a mounted state is not trivial. During manufacture
of a primary insert 18 or a secondary insert 28, the relative positioning of the inner
and outer primary plates 11-15, 16 and the inner and outer secondary plates 21-25,
26 within their respective inserts 18, 28 may vary within certain manufacturing tolerances,
even if made to the same specification. Small differences can lead to a misalignment,
i.e. an offset between the plane of a secondary plate and the plane of the corresponding
primary plate when the secondary insert 28 is brought into a mounted position. Any
such misalignment, even if small, can lead to poor thermal contact. This is of particular
importance at low temperatures such as the operational base temperatures of the third,
fourth and fifth thermal stages 3, 4, 5.
[0045] In order to achieve good thermal contact between corresponding plates in the primary
insert 18 and secondary insert 28, the cryogenic cooling system also comprises adjustment
members (examples of which will be described in further detail below) which cause
the inner primary plates 11-15 and inner secondary plates 21-25 to be brought into
conductive thermal contact when the secondary insert 28 is in a mounted state thus
accommodating a misalignment. The adjustment members may form part of the primary
insert 18 or part of the secondary insert 28 or part of both.
[0046] In Figure 2, the components of the cryogenic cooling system are shown in a mounted
position. Figure 3 provides an exploded view of the cryogenic cooling system according
to the first embodiment with the secondary insert 28 and edge pieces 31-35 removed
from the primary insert 18 to more clearly show the component parts of the system.
Figure 3 shows the edge pieces 31-35, the secondary insert 28 comprising a plurality
of inner secondary plates 21-25 and an outer secondary plate 26 connected by secondary
rods 27, and the primary insert 18 comprising a plurality of inner primary plates
11-15 and an outer primary plate 16 connected by primary rods 17.
[0047] In this embodiment, the cooling apparatus is attached to the primary insert 18. The
cooling apparatus includes a PTR 40, comprising a first PTR stage 41 thermally coupled
to the first inner primary plate 11 of the first thermal stage 1 and a second PTR
stage 42 thermally coupled to the second inner primary plate 12 of the second thermal
stage 2. The cooling apparatus further comprises a dilution unit 8, wherein a still
10 of the dilution unit 8 is thermally coupled to the primary plate 13 of the third
thermal stage 3 and a mixing chamber 9 of the dilution unit 8 is thermally coupled
to the primary plate 15 of the fifth thermal stage 5. In an alternative embodiment,
the cooling apparatus is attached to the secondary insert. For example, the dilution
unit may alternatively be mounted to the inner secondary plates 23, 24, 25 of the
third, fourth and fifth thermal stages 3, 4, 5.
[0048] The inner and outer plates 11-15, 16 of the primary insert 18 are aligned along an
axis 39 extending normal to the inner and outer primary plates 11-15, 16 in a primary
configuration. Similarly, the inner and outer plates 21-25, 26 of the secondary insert
28 are aligned and spatially dispersed along a central axis normal to the inner and
outer plates 21-25, 26 of the secondary insert 28 in a secondary configuration. There
may be an offset between the plane of a secondary plate and the plane of the corresponding
primary plate in the respective primary and secondary configurations, referred to
as a misalignment. Each of the inner secondary plates 21-25 is configured to be brought
into conductive thermal contact with its corresponding inner primary plate 11-15 when
the secondary insert 28 is mounted to the primary insert 18, thus accommodating any
misalignment. Such conductive thermal contact is caused by adjustment members. The
outer secondary plate 26 forms a vacuum seal with the outer primary plate 16, for
example through use of o-rings although any suitable sealing mechanism is possible.
[0049] The installation of the secondary insert 28 into the cryogenic cooling system will
now be described with reference to Figure 3. Firstly, the secondary insert 28 is aligned
with the primary insert 18 in two dimensions, with each inner and outer secondary
plate 21-25, 26 positioned slightly below the corresponding inner and outer primary
plate 11-15, 16. Secondly, the secondary insert 28 is aligned in the third dimension,
wherein the third dimension is parallel to a major axis 39 of the primary insert 18.
The alignment in the third dimension with the primary insert 18 is achieved by raising
the secondary insert 28 such that each inner and outer secondary plate 21-25, 26 is
brought towards its corresponding inner and outer primary plate 11-15, 16 so as to
form conductive thermal contact between each pair of primary and secondary plates.
The outer secondary plate 26 of the outer stage 6 forms a seal with the outer primary
plate 16. The inner secondary plates 21-25 can then be fixed into place. In this embodiment
they are fixed using fastening members, here in the form of screws. The adjustment
members (not shown) cause the inner primary plates 11-15 and inner secondary plates
21-25 to be brought into conductive thermal contact in the mounted state. Finally,
the edge pieces 31-35 are fixed into place, using screws.
[0050] Each edge piece 31-35 is shaped so as to shield lower base-temperature components
from excess radiation. As can be seen from Figure 3, the shape of each edge piece
31-35 is designed to match the shape of each inner secondary plate 21-25 and each
inner primary plate 11-15 to complete each thermal stage 1-5. In an alternative embodiment,
the edge pieces 31-35 can be mounted to the inner primary plates 11-15 without a secondary
insert 28 in place. In another embodiment, the edge pieces are not required. Instead,
each inner secondary plate 21-25 may be shaped so as to complete each thermal stage
1-5 and act as a thermal shield to block radiation between the adjacent stages.
[0051] The secondary insert 28 of the cryogenic cooling system is demountable from the primary
insert 18. Figure 4 shows the cryogenic cooling system in accordance with the first
embodiment, with the secondary insert 28 in a demounted position and the edge pieces
31-35 attached to the corresponding inner primary plates 11-15.
[0052] Whilst the secondary insert 28 is in a demounted position, modifications can be made
to the secondary insert 28 and particularly the experimental services mounted to the
secondary insert 28. This is practically easier for the user to achieve in the demounted
position. Modifications to the secondary insert 28 may include, for example, updating
or testing the experimental services mounted to the secondary insert 28. If desired,
an upgraded secondary insert 28 may then be mounted to the primary insert 18. Furthermore,
it may be advantageous to have more than one secondary insert 28 in order to have
one secondary insert 28 in operation, i.e. in a mounted state and in experimental
use, and one or more secondary inserts 28 on the bench, i.e. in a demounted state.
Whilst in a demounted state, the experimental services on the secondary insert 28
can be modified or upgraded more easily. The experimental services on the demounted
secondary insert 28 can be tested at room temperature, or the secondary insert 28
can be mounted into a donor cryostat to test the experimental services at low temperatures.
The above testing, assembly, modification and upgrades can be performed in parallel
to an experiment being performed in the cryogenic cooling system.
[0053] As described above, the secondary insert 28 forms a tiered assembly. The spatial
distribution of the inner and outer secondary plates 21-25, 26 within the assembly
defines five inter-plate spaces 51-55 as shown in Figure 4: a first inter-plate space
51 between the outer secondary plate 26 and the first inner secondary plate 21, a
second inter-plate space 52 between the first inner secondary plate 21 and the second
inner secondary plate 22, a third inter-plate space 53 between the second inner secondary
plate 22 and the third inner secondary plate 23, a fourth inter-plate space 54 between
the third inner secondary plate 23 and the fourth inner secondary plate 24, and a
fifth inter-plate space 55 between the fourth inner secondary plate 24 and the fifth
inner secondary plate 25.
[0054] In Figure 4, a group of four secondary rods 27 extends across each respective inter-plate
space 51-55 connecting each pair of adjacent secondary plates 21-26. The arrangement
of each group of secondary rods 27 is offset with respect to the adjacent group to
allow each rod from a respective inter-plate space 51-55 to be adjusted or removed
independently. Removal of all of the secondary rods 27 in one of the inter-plate spaces
51-55 allows the secondary insert 28 to be divided into two parts. Two or more plates
of the secondary insert 28 can hence be removed from the remaining plates as a unitary
structure. Figure 5 illustrates a cryogenic cooling system according to the first
embodiment in which the secondary insert 28 is partially demounted.
[0055] In Figure 5 the secondary rods 27 in the fourth inter-plate space 54 have been removed.
The fourth inter-plate space 54 is between the third inner secondary plate 23 and
the fourth inner secondary plate 24, and thus the removal of the above secondary rods
27 allows the fourth inner secondary plate 24 and the fifth inner secondary plate
25 to be demounted from the cryogenic cooling system whilst leaving the remaining
inner and outer secondary plates 21-23, 26 mounted. The fourth and fifth inner secondary
plates 24, 25 remain held together by connecting secondary rods 27, and therefore
this assembly is still self-supporting once it has been demounted from the cryogenic
cooling system. In alternative embodiments, any number of the inner and outer secondary
plates 21-25, 26 can be removed.
[0056] Depending on the experimental circumstances, it may only be necessary to test or
modify only a subset of the secondary plates 21-26 of the secondary insert 28. Partial
removal of the secondary insert 28 is therefore advantageous as it allows for more
flexible preparation and testing of experimental services. In addition, re-installation
of a part of the secondary insert 28 as opposed to the whole secondary insert 28 is
less complex for a user to perform. The cryogenic cooling system can be operated with
the inner secondary plates 21-25 removed. However, if the inner secondary plates 21-24
of any of the first to fourth thermal stages 1-4 are removed, then they should generally
be replaced with blanks to reduce radiation transfer between the thermal stages.
[0057] Experimental services can be mounted to the cryogenic cooling system. Figure 6 illustrates
the cryogenic cooling system according to the first embodiment with experimental services
mounted to the secondary insert 28. Examples of experimental services may include
wiring which may be RF wiring, ultra-high vacuum components, electrical devices (such
as attenuators, filters, circulators or other microwave components, amplifiers, resistors,
transistors, thermometers, capacitors, inductors), or any other experimental services
required for a chosen experiment. The experimental services illustrated in Figure
6 are coaxial wires.
[0058] As described above, secondary inserts may be wholly or partially demounted from a
cryogenic cooling system and inserted into another cryogenic cooling system. There
may be a misalignment between each inner secondary plate 21-25 and the corresponding
inner primary plate 11-15 when the secondary insert 28 is brought into a mounted position,
which can lead to poor thermal contact. In order to ensure good thermal contact, the
cryogenic cooling system comprises adjustment members. Possible adjustment members
will now be described with reference to Figures 7-12.
[0059] Figure 7 schematically illustrates a front view of an inner secondary plate in accordance
with the first embodiment. Although described below in relation to the first inner
secondary plate 21, the description may be applicable to any one or more of the inner
secondary plates 21-25 of the secondary insert 28. The first inner secondary plate
21 has a rigid central part 43. There are flanges 44 along each side of the rigid
central part 43, arranged in the plane of the first secondary plate 21. In this embodiment,
each flange 44 has secondary holes 59 distributed evenly along the length of the flange
44. The holes may be tapped or untapped. A matching series of holes is positioned
on the corresponding primary plate (see Figures 8(a) and 8(b)) so that the first inner
secondary plate 21 can be mounted to the first inner primary plate 11 using screws
or any suitable attachment mechanism.
[0060] The flanges 44 are separated from the rigid central part 43 by a linking portion
45. The linking portion 45 is a relatively thin strip of the first inner secondary
plate 21 extending along the length of the flange 44 and which forms a pivot about
which the flange 44 can move. The first inner secondary plate 21 further accommodates
four receiving holes 46 for positioning the secondary rods 27, although of course
the number of receiving holes 46 may vary depending on the number of secondary rods
27 used.
[0061] In the first embodiment, the flanges 44 are configured to deform when a load is applied
so as to cause the first inner primary plate 11 and the first inner secondary plate
21 to be brought into conductive thermal contact. Localised deformation allows rigid
experimental apparatus to be mounted to the secondary insert 28, such as an ultra-high
vacuum port. Such rigid apparatus may, once mounted, effectively determine the separation
between two or more of the inner or outer secondary plates 21-25, 26. In this embodiment,
the rigid apparatus is mounted to the rigid central part 43 of the first inner secondary
plate 21, and the flanges 44 provide a deformable portion thus forming the adjustment
members. The localised deformation of the flanges 44 accommodates any misalignment
between the first inner primary plate 11 and the first inner secondary plate 21. The
inclusion of a rigid central part 43 of an inner secondary plate advantageously allows
rigid experimental apparatus to remain unaffected by any adjustment required whilst
ensuring effective thermalisation between the secondary insert 28 and the primary
insert 18.
[0062] Figures 8(a) and 8(b) schematically illustrate a side view of a part of a cryogenic
cooling system in accordance with the first embodiment during a mounting process.
Figure 8(a) illustrates a portion of the secondary insert 28 in a demounted state
and Figure 8(b) illustrates the portion of the secondary insert 28 in a mounted state,
with the adjustment member in use. Figures 8(a) and 8(b) depict portions of the first
inner secondary plate 21, the second inner secondary plate 22, the first inner primary
plate 11 and the second inner primary plate 12. However, the description applies to
any adjacent inner plates in the secondary insert 28 and the corresponding plates
in the primary insert 18.
[0063] The first inner secondary plate 21 comprises a rigid central part 43, a flange 44
and a linking portion 45. The second secondary plate 22 comprises a rigid central
part 43', a flange 44' and a linking portion 45'. Primed reference numerals are used
to designate similar apparatus features between the second inner secondary plate 22
and the first inner secondary plate 21. The first and second inner secondary plates
21, 22 both take the form shown by Figure 7. The first inner primary plate 11 is connected
to the second inner primary plate 12 by a primary rod 17. Typically, more than one
primary rod 17 will be used to connect adjacent plates of the primary insert 18, but
only one is shown here for clarity.
[0064] Figure 8(a) schematically illustrates a portion of the secondary insert 28 and the
corresponding portion of the primary insert 18 when the secondary insert 28 is in
a demounted state. In a demounted state, the separation between the first inner secondary
plate 21 and the second inner secondary plate 22 is
d2. The separation between the first inner primary plate 11 and the second inner primary
plate 12 is
d1, wherein
d1 >
d2. In a different example, the misalignment may be in the opposite direction, i.e
d1 <
d2. The relative lateral positioning in Figure 8(a) is illustrative only, and is to
show the vertical misalignment clearly. The misalignment is between the first inner
secondary plate 21 and the first inner primary plate 11. The first and second inner
primary plates 11, 12 comprise a stepped portion along the periphery through which
primary holes 69, 69' extend. The secondary holes 59, 59' in the first and second
inner secondary plates 21, 22 are configured to align with the primary holes 69, 69'
in the first and second inner primary plates 11, 12 respectively.
[0065] In an alternative embodiment, the flanges may be positioned on the plates of the
primary insert 18, instead of the secondary insert 28. This may be particularly advantageous
if there are multiple interchangeable secondary inserts 28 for a cryogenic cooling
system, some of which may not comprise adjustment members. In another alternative
embodiment, the flanges 44 may be positioned on the plates of the primary insert 18
and the secondary insert 28. This may advantageously allow a larger possible misalignment
as the deformation could occur on both sides.
[0066] Figure 8(b) schematically illustrates the portion of the secondary insert 28 and
the corresponding portion of the primary insert 18 of Figure 8(a) when the secondary
insert 28 is in a mounted state. In Figure 8(b) the secondary holes 59, 59' are aligned
with the primary holes 69, 69'. The flange 44 and the linking portion 45 are in a
deformed position, deformed to cause the first inner primary plate 11 and the first
inner secondary plate 21 to be brought into conductive thermal contact. The flange
44 is thus in area contact with the first inner primary plate 11 along the stepped
portion of the first inner primary plate 11. The planar regions of the stepped portion
of the first inner primary plate 11 conform to the flange 44 of the first inner secondary
plate 21.
[0067] In this embodiment, the deformation of the flanges 44, 44' can accommodate the misalignment
between
d1 and
d2 whilst the rigid central parts 43, 43' of the first inner secondary plate 21 and
the second inner secondary plate 22 remain in a fixed position with respect to each
other. The first inner primary plate 11 and the second inner primary plate 12 also
remain in a fixed position with respect to each other before and after the mounting
process.
[0068] Figures 9(a) and 9(b) schematically illustrate a side view of a part of a cryogenic
cooling system in accordance with a second embodiment, showing a portion of a secondary
insert 128 in a mounted state, with an adjustment member in use. The cryogenic cooling
system takes a similar form to that described in the first embodiment, although the
adjustment members provided are different. Each of Figures 9(a) and 9(b) show a first
inner secondary plate 121 connected to a second inner secondary plate 122 by a secondary
rod 127 and a first inner primary plate 111 connected to a second inner primary plate
112 by a primary rod 117. Typically, further primary rods 117 and further secondary
rods 127 are used, but for clarity only one is shown in Figures 9(a) and 9(b). With
the secondary insert 128 shown in a mounted position, the secondary holes 159, 159'
are aligned with the primary holes 169, 169'.
[0069] In the second embodiment, the secondary rods 127 are configured to deform when a
compressive or tensile load is applied so as to adjust the separation between the
adjacent inner secondary plates 121, 122. This movement accommodates any misalignment
between the corresponding plates of the primary and secondary inserts 118, 128. In
this embodiment, the primary rods 117 are rigid and therefore the separation between
adjacent plates in the primary insert 118 is fixed. The secondary rods 127 are formed
from stainless steel and curved to allow deformation as described. The deformation
of the secondary rods 127 causes each of the inner secondary plates 121-125 to be
brought into conductive thermal contact with the corresponding inner primary plates
111-115.
[0070] In Figure 9(a), the separation between the first inner secondary plate 121 and the
second inner secondary plate 122 in a demounted state,
d2, is less than the separation between the first inner primary plate 111 and the second
inner primary plate 112,
d1, i.e.
d2 <
d1. The secondary rod 127 is in a first position 147, indicated in Figure 9(a) using
dashed lines, when the secondary insert 128 is in a demounted state. The secondary
rods 127 are configured to be extended in response to a tensile load to a second position
148, indicated in Figure 9(a) using a solid line, in which the first and second inner
secondary plates 121, 122 are separated further to enable good thermal contact between
the first and second inner primary plates 111, 112 respectively along the contact
surfaces.
[0071] In Figure 9(b), the separation between the first inner secondary plate 121 and the
second inner secondary plate 122 in a demounted state,
d2, is greater than the separation between the first inner primary plate 111 and the
second inner primary plate 112,
d1, i.e.
d2 >
d1. The secondary rod 127 is in a first position 147, indicated in Figure 9(b) using
dashed lines, when the secondary insert 128 is in a demounted state. The secondary
rods 127 are configured to be compressed in response to a compressive load to a third
position 149, indicated in Figure 9(b) using a solid line, in which the first and
second inner secondary plates 121, 122 are brought into good thermal contact with
the first and second inner primary plates 111, 112 respectively.
[0072] In the second embodiment as described above with reference to Figures 9(a) and 9(b),
the secondary rods 127 can accommodate the misalignment between corresponding inner
plates of the primary insert 118 and secondary insert 128 of the cryogenic cooling
system. The secondary rods 127 are configured to adjust the separation between adjacent
secondary plates in order to bring each plate of the secondary insert 128 into alignment
with each plate of the primary insert 118.
[0073] In an alternative embodiment, the primary rods may be configured to deform when a
compressive or tensile load is applied, as described above in relation to the secondary
rods 127, and the secondary rods may be rigid thus fixing the position of the inner
and outer secondary plates with respect to one another. This may make the secondary
insert more secure in a demounted state.
[0074] Figures 10(a) and 10(b) schematically illustrate a side view of a part of a cryogenic
cooling system in accordance with a third embodiment. Similar to the second embodiment
(Figures 9(a) and 9(b)) and unlike the first embodiment (Figures 8(a) and 8(b)), the
third embodiment comprises an adjustment member configured to adjust the separation
between adjacent plates of an insert. Figure 10(a) illustrates a portion of a secondary
insert 228 in a demounted state, whereas Figure 10(b) illustrates the portion of the
secondary insert 228 in a mounted state, with the adjustment member in use. Figures
10(a) and 10(b) depict a first inner secondary plate 221, a second inner secondary
plate 222, a first inner primary plate 211 and a second inner primary plate 212.
[0075] In Figures 10(a) and 10(b), the first inner secondary plate 221 is connected to the
second inner secondary plate 222 by a secondary rod 227. An upper secondary rod 227'
connects the first inner secondary plate 221 to the outer secondary plate (not shown).
A lower secondary rod 227" connects the second inner secondary plate 222 to the third
inner secondary plate (not shown). Each of the secondary rods 227, 227', 227" comprises
a shoulder 229, 229" provided at the proximal end of each rod 227, 227', 227" and
adapted to receive a grub screw 230, 230'. The first inner primary plate 211 is connected
to the second inner primary plate 212 by a primary rod 217. An upper primary rod 217'
connects the first inner primary plate 211 to the outer primary plate 216 (not shown).
A lower primary rod 217" connects the second inner primary plate 212 to the third
inner primary plate 213 (not shown).
[0076] Figure 10(a) schematically illustrates a portion of the secondary insert 228 and
the corresponding portion of the primary insert 218 when the secondary insert 228
is in a demounted state. Secondary holes 259, 259' are configured to align with primary
holes 269, 269' when the secondary insert 228 is in a mounted state, with a fastening
member extending between them. The primary holes 269, 269' and/or the secondary holes
259, 259' may be threaded, or may form clearance holes, for example where the fastening
member is used in conjunction with a backing nut. In Figure 10(a), the separation
between the first inner secondary plate 221 and the second inner secondary plate 222
in a demounted state,
d2, is greater than the separation between the first inner primary plate 211 and the
second inner primary plate 212,
d1, i.e.
d2 >
d1. The relative lateral positioning in Figure 10(a) is illustrative only, and is to
show the vertical misalignment clearly. The misalignment is between the second inner
secondary plate 222 and the second inner primary plate 212.
[0077] In a demounted state, the first inner secondary plate 221 and the second inner secondary
plate 222 are positioned on the shoulders 229, 229" of the secondary rod 227 and lower
secondary rod 227" respectively. A first grub screw 230 is positioned between the
secondary rod 227 and the upper secondary rod 227'. An upper portion of the secondary
rod 227 and a lower portion of the upper secondary rod 227' are tapped so as to engage
with the first grub screw 230. A second grub screw 230' is positioned between the
secondary rod 227 and the lower secondary rod 227". An upper portion of the lower
secondary rod 227" and a lower portion of the secondary rod 227 are tapped so as to
accommodate the second grub screw 230'. It is this combination of the tapped portion
of a secondary rod and the corresponding grub screw with which it engages that forms
the adjustment member in this embodiment. In an alternative embodiment, the primary
rods may be fitted with an adjustment mechanism as described for the secondary rods
or both the primary rods and the secondary rods may be fitted with such adjustment
mechanisms.
[0078] Figure 10(b) schematically illustrates the portion of the secondary insert 228 and
the corresponding portion of the primary insert 218 as illustrated in Figure 10(a)
when the secondary insert 228 is in a mounted state. The secondary holes 259, 259'
and the primary holes 269, 269' are aligned, and the corresponding plates are thermally
linked with a high thermal conductance. The separation between the first inner secondary
plate 221 and the second inner secondary plate 222 is adjusted to align with the separation
between the first inner primary plate 211 and the second inner primary plate 212.
In this embodiment, the misalignment is accommodated by separating the second inner
secondary plate 222 from the shoulder 229". In some embodiments this could be achieved
by rotation of the secondary rod 227. In the present embodiment the act of adjusting
a fastening member extending through primary holes 269' into the corresponding secondary
holes 259', lifts the second inner secondary plate 222 off the shoulder 229". It should
be appreciated therefore that unlike in the first and second embodiments, the adjustment
members of the third embodiment facilitate movement of the second inner secondary
plate 222 with respect to the secondary rod 227, along the direction of the secondary
rod 227. Consequently, a thermalising shim 238 is positioned between the secondary
rod 227 and the second inner secondary plate 222. The thermalising shim 238 provides
mechanical support and a thermal connection between the secondary rod 227 and the
second inner secondary plate 222, and will be further discussed in detail with reference
to Figure 13.
[0079] Figure 11 illustrates a cross-sectional view of a portion of a secondary insert plate
according to the third embodiment as illustrated in Figures 10(a) and 10(b). Although
the following describes the second inner secondary plate 222, the description may
apply to any of the inner secondary plates. Figure 11 shows a second inner secondary
plate 222, a secondary rod 227 and a lower secondary rod 227". There is a first threaded
insert 219 arranged between the secondary rod 227 and the second inner secondary plate
222. The first threaded insert 219 extends into the hollow secondary rod 227 at the
proximal end and extends into the second inner secondary plate 222 at the distal end.
A second threaded insert 220 is arranged between the lower secondary rod 227" and
the second inner secondary plate 222. The second threaded insert 220 has a shoulder
229" portion at its proximal end, which extends into the second inner secondary plate
222. At its distal end the second threaded insert 222 extends into the hollow lower
secondary rod 227".
[0080] In this embodiment, the first threaded insert 219 and the second threaded insert
220 are threaded or tapped so as to accommodate the second grub screw 230'. In alternative
embodiments, the grub screw can be a set screw or any screw suitable for adjusting
the separation between the secondary rod 227 and the lower secondary rod 227". The
first threaded insert 219 and the second threaded insert 220 are formed from a material
with a high thermal conductivity at the operational base temperature of the relevant
thermal stage, such as brass or copper. A thermalising shim 238 is again positioned
between the secondary rod 227 and the second inner secondary plate 222. This is also
visible in Figure 12, which provides a perspective view of a portion of a demounted
secondary insert 228 in accordance with the third embodiment. In Figure 12, experimental
services are mounted to the secondary insert 228. In particular, the experimental
services shown are coaxial wires connected to the second inner secondary plate 222
and the first inner secondary plate 221.
[0081] Figure 13 schematically illustrates a cross-sectional view of a part of a cryogenic
cooling system in accordance with the third embodiment, depicting the deformation
of the thermalising shim 238 when the secondary insert 228 is in a mounted state.
The inner secondary plates are moveable within the secondary insert 228 in the direction
of the secondary rods to accommodate a misalignment. In Figure 13, the first inner
secondary plate 221 is shown with two secondary rods 227 and two upper secondary rods
227'. The corresponding primary plate is not shown for clarity.
[0082] A thermalising shim 238 connects the secondary rods 227, 227' to the first inner
secondary plate 221, providing mechanical stability to the arrangement when the first
inner secondary plate 221 is moved along the secondary rods 227, 227'. In this embodiment,
the thermalising shim 238 is formed from a material having a high thermal conductivity
at the operational base temperature of the relevant thermal stage, such as brass or
copper, and further provides effective thermalisation of the secondary rods 227, 227'.
The thermalising shim 238 is configured to thermally couple the ends of the secondary
rods 227' to the inner secondary plate 221. Advantageously, thermalisation of the
secondary rods 227 and primary rods 217 at each thermal stage 201-205 reduces the
time required to cool the cryogenic cooling system from room temperature to an operational
base temperature. It also reduces any unwanted heat transfer between a warm end of
the secondary insert and a cold end along the secondary rods 227. This is achieved
by increasing the thermal conductance between the secondary rods 227 and the secondary
plates, in particular where relative movement between these components is possible.
[0083] The grub screw 230 has a radial protrusion around which the thermalising shim 238
is positioned. The outer holes in the thermalising shim 238 are slotted, allowing
movement of the shim perpendicular to the secondary rods 227, 227' as indicated by
the arrows. When positioned, the thermalising shim 238 is held in place between the
first and second threaded inserts 219, 220 by a clamping force. The thermalising shim
is also fastened securely to the first inner secondary plate 221 using shim screws
267. The thermalising shim 238 is flexible such that it maintains physical contact
with the first inner secondary plate 221 and the secondary rods 227, 227', ensuring
effective thermalisation of the secondary rods 227, 227' when the first inner secondary
plate 221 is moved with respect to the secondary rods 227, 227'. This deformation
of the thermalising shim 238 is visible in Figure 13.
[0084] Figure 14 illustrates exemplary secondary inserts 28', 28", 28‴ for use with primary
inserts in accordance with the previous embodiments. In each case, a number of ports
are shown which are axially aligned between plates. However, as shown the secondary
insert can take a variety of forms. It may be advantageous to have more than one secondary
insert wherein one of the secondary inserts has a different arrangement of ports.
In this case, the same cryogenic cooling system could be used for more than one type
of experiment, by switching one secondary insert configured with a first arrangement
for another secondary insert configured with a second arrangement.
[0085] In further embodiments any combination of the adjustment members previously described
may be used alone or in combination.
[0086] As will be appreciated, a cryogenic cooling system is therefore provided in which
a secondary insert can be demounted from the system whilst achieving effective thermalisation
in a mounted position. The removal of the secondary insert allows for remote assembly,
testing and set-up. Furthermore, the system has additional flexibility due to the
ability to provide modular upgrades in the form of an upgraded secondary insert. The
effective thermalisation, which is important for low temperature experiments, is achieved
using dedicated adjustment members as described.
[0087] Further exemplary embodiments of the present disclosure are set out in the following
numbered clauses:
Numbered clause 1. A cryogenic cooling system comprising: a primary insert comprising:
a plurality of primary plates, each primary plate having a primary contact surface;
and one or more primary connecting members arranged so as to connect the plurality
of primary plates; a demountable secondary insert comprising: a plurality of secondary
plates, each secondary plate having a secondary contact surface; and one or more secondary
connecting members arranged so as to connect the plurality of secondary plates such
that the secondary insert is self-supporting; and one or more adjustment members;
wherein the one or more adjustment members are configured such that, when the secondary
insert is mounted to the primary insert, the adjustment members cause the primary
and secondary contact surfaces of the respective primary and secondary plates to be
brought into conductive thermal contact.
Numbered clause 2. A system according to clause 1, wherein the one or more adjustment
members form part of one or both of the primary insert and the secondary insert.
Numbered clause 3. A system according to clause 1 or clause 2, wherein the said conductive
thermal contact is provided by area contact between conformal planar regions of the
respective primary and secondary contact surfaces.
Numbered clause 4. A system according to any of clauses 1 to 3, wherein the one or
more adjustment members are configured to accommodate a misalignment between each
of the plurality of secondary plates of the demountable secondary insert and the corresponding
primary plate of the primary insert.
Numbered clause 5. A system according to clause 4, wherein the misalignment is less
than 2 millimetres, preferably less than 1 millimetre.
Numbered clause 6. A system according to clause 4 or clause 5, wherein when the secondary
insert is in a demounted state, the secondary plates are spatially positioned with
respect to one another in a secondary configuration, and the primary plates of the
primary insert are spatially positioned with respect to one another in a primary configuration;
and wherein the misalignment is the offset between the plane of a secondary plate
and the plane of the corresponding primary plate in the respective primary and secondary
configurations.
Numbered clause 7. A system according to clause 6, wherein the respective primary
and secondary configurations are maintained when the demountable secondary insert
is in a mounted state.
Numbered clause 8. A system according to any of the preceding clauses, wherein operation
of the adjustment member does not change the separation between adjacent primary plates
of the primary insert or adjacent secondary plates of the secondary insert.
Numbered clause 9. A system according to any of the preceding clauses, wherein the
one or more adjustment members comprise one or more deformable members forming part
of a respective primary plate or secondary plate.
Numbered clause 10. A system according to clause 6, wherein the one or more adjustment
members cause one or both of the primary or secondary configurations to be adjustable
so as to cause the conductive thermal contact.
Numbered clause 11. A system according to any of clauses 1 to 6 or clause 10, wherein
the one or more adjustment members are configured to change the separation between
adjacent primary plates or adjacent secondary plates.
Numbered clause 12. A system according to clause 11, wherein the one or more adjustment
members form at least part of one or more of the primary connecting members or secondary
connecting members.
Numbered clause 13. A system according to clause 11 or clause 12, wherein the one
or more adjustment members is configured to allow movement of the one or more primary
plates with respect to the one or more said primary connecting members.
Numbered clause 14. A system according to clause 13, further comprising one or more
primary shims, each said primary shim thermally coupling a said primary plate to one
or more said primary connecting members and configured to allow movement of the said
primary plate with respect to the said one or more primary connecting members.
Numbered clause 15. A system according to any of clauses 11 to 14, wherein the one
or more adjustment members is configured to allow movement of the one or more secondary
plates with respect to the one or more said secondary connecting members.
Numbered clause 16. A system according to clause 15, further comprising one or more
secondary shims, each said secondary shim thermally coupling a said secondary plate
to one or more said secondary connecting members and configured to allow movement
of the said secondary plate with respect to the said one or more secondary connecting
members.
Numbered clause 17. A system according to any of clauses 11 to 16, wherein the primary
or secondary connecting members are rotatable so as to change the separation between
adjacent primary plates or adjacent secondary plates using the one or more adjustment
members.
Numbered clause 18. A system according to clause 11 or clause 12, wherein the one
or more adjustment members form respective flexible portions of the primary or secondary
connecting members.
Numbered clause 19. A system according to any of the preceding clauses, wherein one
or more of the plurality of secondary plates is configured to accommodate experimental
apparatus.
Numbered clause 20. A system according to any of the preceding clauses, wherein the
primary insert comprises a dilution refrigerator, a helium-3 refrigerator, or a 1
kelvin pot.
Numbered clause 21. A system according to any of the preceding clauses, wherein one
or more of the secondary connecting members are removable such that two or more of
the plurality of secondary plates can be detached from the demountable secondary insert
as a unitary, self-supporting assembly.
Numbered clause 22. A demountable secondary insert for use in a cryogenic cooling
system according to any of the preceding clauses.
Numbered clause 23. A method of operating the system of any of clauses 1 to 21, wherein
the demountable secondary insert comprises a first secondary plate, a second secondary
plate and a third secondary plate, a first secondary connecting member connecting
the first secondary plate to the second secondary plate, and a second secondary connecting
member connecting the second secondary plate to the third secondary plate, and wherein
the primary insert comprises three primary plates, each said primary plate corresponding
to a respective secondary plate of the secondary insert, the method comprising: mounting
the secondary insert to the primary insert such that secondary plates are conductively
thermally coupled to the corresponding primary plates using the one or more adjustment
members; and partially demounting the secondary insert from the primary insert, wherein
partially demounting the secondary insert comprises: removing the first secondary
connecting member from the secondary insert; and removing the second secondary plate,
the third secondary plate and the second secondary connecting member from the primary
insert as a unitary self-supporting assembly, without removing the first secondary
plate from the corresponding plate of the primary insert.
1. A cryogenic cooling system comprising:
a primary insert (118) comprising:
a plurality of primary plates (111, 112), each primary plate having a primary contact
surface; and
one or more primary connecting members (117) arranged so as to connect the plurality
of primary plates;
a demountable secondary insert (128) comprising:
a plurality of secondary plates (121, 122), each secondary plate having a secondary
contact surface; and
one or more secondary connecting members (127) arranged so as to connect the plurality
of secondary plates (121, 122) such that the secondary insert (128) is self-supporting;
cooling apparatus attached to the secondary insert; and
one or more adjustment members;
wherein the one or more adjustment members are configured such that, when the secondary
insert is mounted to the primary insert, the adjustment members cause the primary
and secondary contact surfaces of the respective primary and secondary plates to be
brought into conductive thermal contact.
2. A system according to claim 1, wherein the cooling apparatus comprises a dilution
unit (8).
3. A system according to claim 1 or 2, wherein the cooling apparatus comprises a mechanical
refrigerator (40), such as a pulse tube refrigerator.
4. A system according to any of the preceding claims, wherein the cooling apparatus is
mounted to one or more of the secondary plates.
5. A system according to any of the preceding claims, wherein the one or more adjustment
members form part of one or both of the primary insert (118) and the secondary insert
(128).
6. A system according to any of the preceding claims, wherein the said conductive thermal
contact is provided by area contact between conformal planar regions of the respective
primary and secondary contact surfaces.
7. A system according to any of the preceding claims, wherein the one or more adjustment
members are configured to accommodate a misalignment between each of the plurality
of secondary plates of the demountable secondary insert and the corresponding primary
plate of the primary insert.
8. A system according to any of the preceding claims, wherein the one or more adjustment
members comprise one or more deformable members forming part of a respective primary
plate or secondary plate.
9. A system according to any of claims 1 to 7, wherein the one or more adjustment members
are configured to change the separation between adjacent primary plates or adjacent
secondary plates.
10. A system according to any of claim 9, wherein the one or more adjustment members form
at least part of one or more of the primary connecting members or secondary connecting
members.
11. A system according to claims 9 or 10, wherein the one or more adjustment members is
configured to allow movement of the one or more secondary plates with respect to the
one or more said secondary connecting members.
12. A system according to claim 11, further comprising one or more secondary shims, each
said secondary shim thermally coupling a said secondary plate to one or more said
secondary connecting members and configured to allow movement of the said secondary
plate with respect to the said one or more secondary connecting members.
13. A system according to any of claims 9 to 12, wherein the primary or secondary connecting
members are rotatable so as to change the separation between adjacent primary plates
or adjacent secondary plates using the one or more adjustment members.
14. A system according to claims 9 or 10, wherein the one or more adjustment members form
respective flexible portions of the primary or secondary connecting members.
15. A system according to any of the preceding claims, wherein one or more of the secondary
connecting members are removable such that two or more of the plurality of secondary
plates can be detached from the demountable secondary insert as a unitary, self-supporting
assembly.
16. A demountable secondary insert (128) for use in a cryogenic cooling system according
to any of the preceding claims, wherein the demountable secondary insert comprises
cooling apparatus.
17. A method of operating the system of any of claims 1 to 15, the method comprising mounting
the secondary insert (128) with the cooling apparatus attached thereto to the primary
insert (118).
18. A method according to claim 17, wherein mounting the secondary insert comprises bringing
one or more of the secondary plates (121, 122) into contact with a corresponding said
primary plate (111, 112).
19. A method of operating the system of any of claims 1 to 15, wherein the demountable
secondary insert comprises a first secondary plate, a second secondary plate and a
third secondary plate, a first secondary connecting member connecting the first secondary
plate to the second secondary plate, and a second secondary connecting member connecting
the second secondary plate to the third secondary plate, and wherein the primary insert
comprises three primary plates, each said primary plate corresponding to a respective
secondary plate of the secondary insert, the method comprising:
mounting the secondary insert to the primary insert such that secondary plates are
conductively thermally coupled to the corresponding primary plates using the one or
more adjustment members; and
partially demounting the secondary insert from the primary insert, wherein partially
demounting the secondary insert comprises:
removing the first secondary connecting member from the secondary insert; and
removing the second secondary plate, the third secondary plate and the second secondary
connecting member from the primary insert as a unitary self-supporting assembly, without
removing the first secondary plate from the corresponding plate of the primary insert.